There exist shock-absorbing or anti-shock systems in timepieces for protecting the staffs of the wheel sets. A first system is a lyre-type system, i.e. the plate or bridge is provided with a hole, through which the pivot shank of a staff can pass. This hole serves as receptacle for a support that is pierced at its centre, in which a setting is arranged. This setting carries a pierced stone and an endstone, wherein the whole unit is placed under stress by a lyre spring arranged between the support, which has edges serving as support points, and the setting. Another system is the “pare-chute” system, in which the pivots of the balance are configured in order to give them the form of a cone and hold them in place by means of a small turning pin of corresponding shape mounted on a spring blade.
Watchmaking anti-shock systems are generally formed by mechanical springs and are also dimensioned in the traditional manner following practical rules regarded as the best compromise between mechanical stability during operation and resistance to mechanical deformations.
In particular, anti-shock elements of the balance spring, i.e. para-chute and lyre type elements, are dimensioned so as not to be activated until relatively significant shock accelerations (between 200 and 500 times gravity) because of the prestressing of the spring. Beyond this threshold value the spring can be deformed and absorb a portion of the energy of the shock. However, because of the poor mechanical absorption of the metal blades used as anti-shock elements most of the energy is returned to the balance. Local deformation of the pivot of the balance is therefore highly probable, even in the case of relatively light shocks. This deformation, which has a considerable impact on the chronometric precision of the watch, is generally ignored because the standard certifying the chronometric stability of a watch COSC following a shock of one metre is not very severe (60 s/d).
There is therefore a need to improve the chronometric stability of the watch after a shock.